Cheapest Video Card to run Motion?

I am currently running a dual 1.25ghz G4 and need to upgrade my video card to run Motion. So, my question is what is the cheapest video card that will work with motion and where can I buy it. I have searched for the nvidia geforce 5200 fx for macs, but i can not find it anywhere and same with the ati radeon 9600 pro. If anyone knows where I can buy one and for how much let me know please.
Thanks!

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